1. Field of the Invention
The present invention relates to a data recording/reproducing apparatus capable of recording/reproducing desired data by use of a recording medium.
2. Description of the Related Art
Of data recording/reproducing apparatuses such as optical disc apparatuses and optical card apparatuses, there is a data recording/reproducing apparatus for recording/reproducing data by use of a non-rewritable recording medium.
If data is doubly written on a data-recorded region, such as a track or a sector, of such a non-rewritable recording medium, not only the previously recorded data but also newly recorded data cannot be reproduced. In order to prevent the occurrence of this undesirable situation, it is necessary to exactly check in advance whether or not data has been stored on the target track or sector.
Published Unexamined Japanese Patent Application No. 63-53724 discloses a technique of determining whether data is recorded on a recording region by counting the number of pits in the recording region and detecting whether or not the counted value is above a predetermined value, thus preventing overwriting of data.
In this type of data recording/reproducing apparatus, however, the presence/absence of data is determined only on the basis of the fact that the number of pits is or is not above a predetermined value. A recording area on which data is normally recorded cannot be distinguished from a recording area on which data is doubly written (overwritten). Consequently, when the data on the overwritten area is reproduced, normal reproduction cannot be effected and the reproduction must be retried more times than required. This degrades a data reproduction access time.
On the other hand, in some cases, data on an unneeded recorded area or sector is intentionally destroyed by overwrite, for example, in order to keep secrecy. This is called data erasure. In this case, too, it is necessary to check, in advance, whether a target track or sector has been subjected to data erasure. In connection with this, there is a concern that the number of pits cannot be counted because of the destruction of pits and the "non-recorded state" of the track or sector may be determined, although the data has actually been erased.